#include<iostream>
#include<cmath>
using namespace std;

struct Point{
	double x,y;
};

int main()
{
	struct Point p1,p2;
	
	cin>>p1.x>>p1.y;
	cin>>p2.x>>p2.y;
	
	double distance;
	
	distance = sqrt(pow((p1.x-p2.x),2)+pow((p1.y-p2.y),2));
	cout<<distance;
	
	return 0;
}
